Polyimide coatings derived from the curing (imidization) of polyamic acids are well known. These imidized coatings, typically prepared from aromatic polyamic acids display high temperature stability and accordingly are useful as insulative and adhesive coatings on electrical circuitry and in high temperature laminates.
It has recently been discovered that polyimides based on 2,2-bis[4-(aminophenoxy)phenyl]hexafluoropropane provide superior coatings for bearings as well as for piston skirts and other sliding parts. See for example U.S. Pat. Nos. 4,816,516 and 4,831,977. These coatings, defined as "lubricant films" are particularly effective (as to wear and adhesion) for reciprocating engine surfaces where substantially continuous frictional contact occurs.
In U.S. Pat. No. 4,293,684 the use of aromatic polyetherimides as injection moldable compositions has been disclosed as yielding molded parts displaying an undesirable affinity for adhering to the working surfaces of the mold. This results in complications to fabrication and defects in the surface characteristics of the molded part.
The present invention is based on the discovery that the fluorine-containing aromatic polyimides and their polyamic acid precursors can be used to treat the working surface of a mold to improve its release characteristics.